If you’ve been in a relationship with the same person long enough, you realize that, though some things will inevitably stay the same (your inability to decide where you want to eat, your partner’s penchant for corny dad jokes), others are bound to change over time.

The relationship can’t mature if both of you aren’t open to change and willing to grow. When things between you remain stagnant for too long, it doesn’t bode well for your future together.

“The same habits, communication skills and interpersonal dynamics that worked for a couple in their early 20s probably won’t, and shouldn’t, work for the same couple 25 years later,” said psychotherapist Kathleen Dahlen deVos.

We asked deVos and other therapists to identify some of the ways the happiest couples evolve over time and how those changes make for a more satisfying relationship.

1. They encourage each other to have their own lives separate from the relationship.

In the early infatuation stage of a relationship, couples tend to spend a lot of time doing things as a twosome, sometimes putting their individual lives on the back burner. But as time goes on, the happiest couples learn that they don’t need to be attached at the hip. Instead, they prioritize their independence, striking a balance between “me” time and “we” time. They allow each other to develop as individuals, each with their own set of hobbies, interests and friendships outside of the primary relationship, deVos told HuffPost.

“When couples rely solely on each other to meet all of their emotional intimacy and social needs, this ‘merging’ can stifle healthy personal growth or threaten to slip into co-dependency,” deVos said. “Rather, these couples encourage each other to define themselves as individuals within a relationship rather than being defined by the relationship itself.”

2. They become better communicators.

Strong communication is the foundation of any happy, healthy relationship — a partnership can’t thrive without it. That means honing your ability to express your needs and desires to your partner and also learning how to be a better, more compassionate listener, too.

“Learning to speak your truth respectfully and genuinely listening to your partner’s feelings, thoughts and needs can be particularly challenging in times of conflict or distress, yet this is one of the biggest predictors of a couple’s health and happiness over time,” marriage and family therapist Andrea Wachter said.

The healthiest couples are in the habit of dealing with conflict head-on rather than ignoring an issue and letting resentment build.

“Mature couples have communication down pat,” psychotherapist Patrick Schultz said. “They know how to approach their partner and talk about anything and everything they need. The partner does not have to be fearful that something will catch them off guard.”

3. They find new ways to keep the relationship exciting.

It’s easy to get trapped in a ho-hum routine, focusing only on what needs to get done at work, with the kids or around the house, never leaving any time for fun. The happiest couples continue to look for new ways to keep the spark alive — checking out a new restaurant, volunteering with a different charity or, heck, experimenting with a new sex position — instead of settling for a life of blah.

“Couples that successfully mature over time find ways to stay engaged and excited about each other and about life together,” said marriage and family therapist Jon-Paul Bird.

But you don’t always have to reinvent the wheel, Bird added.

“Remember to do the little things: flowers, love notes, midday calls and the ‘just becauses.’ They go a long way to remind your partner that they still occupy space in your thoughts.”

4. They dig deep because they want to know each other on a more intimate level.

By the time you get married, particularly if you dated for a long time, it may feel like you know all there is to know about your partner: their weird habits, their dream job, their family dynamics. Instead of getting complacent, the happiest couples stay curious about each other for years to come, always looking for opportunities to be vulnerable and connect on a deeper level.

“No matter how well we know someone (or think we do), they can always surprise us, and we have to allow room for them to,” deVos said. “Curiosity is one of the ingredients that fuels early relationships — the eager desire to learn all about this new person. Solid long-term couples also understand that there is always something new to discover about their partner.”

5. They honor each other’s changing needs, giving each other room to grow.

Watching your partner change (even when the changes are positive) can be a little unnerving for some. “What if they go down this new path and leave me in the dust?” you may wonder. But instead of resisting those changes, the happiest couples empower their partner to branch out and recognize that it’s actually healthy for the relationship.

“For example, two people might start out loving outdoor activities and, in later years, one of them begins to value — or need — more indoor time. Regardless of the reasons for the changes, it is critical to a long-term healthy bond that we honor each other’s needs, especially when they don’t match our own,” Wachter said.

And that applies to each partner’s individual values, too, said associate marriage and family therapist Kate Stoddard of Wellspace SF.

“Couples who have the ability to be flexible when it comes to evaluating their individual values year after year will fare much better than those who are rigid and uncompromising,” Stoddard said.

6. They keep setting new goals and helping each other achieve them.

Whatever your goals in life may be — changing careers, adopting a child, buying a house, running a half marathon, taking up calligraphy — a great partner will be firmly in your corner. It doesn’t matter if the goal is an individual one (like writing a book) or a shared one (like starting a family) because couples in the healthiest relationships recognize that both are equally important. After one goal is achieved, these couples don’t just rest on their laurels. Rather, they encourage each other to strive for more by setting new goals and helping each other reach them.

“You work together to complement each other and support each other on the journey to your bigger goals for life and partnership,” Schultz said. “By working together on these goals, you get the collective nature of two people invested in a common objective, which makes it far more likely that you will achieve this goal in a faster and more efficient way.”