I married my high-school sweetheart. This is what we've learned over 18 years together about keeping our relationship strong.

• My husband and I met when we were 16 and in high school.
• We were married by the time we were 20.
• We've changed over the past 18 years — but we've grown together instead of apart.

I met my husband when we were both 16, and we married at 20, a fact that in hindsight absolutely boggles my mind. People often marvel at our relationship, remembering their own high-school and early-college years and their relationship mishaps during that time.

I marvel at it too, remembering the kids we were when we met and all the iterations of ourselves we've cycled through over our 18-year relationship.

So how is it that we've grown together instead of apart when we committed to one another at such an inadvisably young age?

I wasn't a particularly mature teenager — if anything, the way I approached my relationships seemed worse than the way my peers did. I was, despite my best efforts, desperately clingy. I overanalyzed every romantic interaction to my detriment. I had the communicative skills of a goldfish. I was the sort of teenage girl who really wanted to project "cool, laid-back girlfriend" but secretly seethed with insecurities and unspoken expectations.

Part of our success has been luck, surely, but I like to think we've figured out some important things about marriage along the way. We've grown up together and grown closer, turning our high-school relationship into a partnership that has stood the test of time — even as major parts of our identities have shifted.

We've been through a lot of experiences that can derail a marriage. We've forged new belief systems, became parents, brought home pets, switched career paths, dealt with miscarriages and job loss and pets dying. Our friend group has changed. Our bodies have changed.

We have changed. And yet we have persevered, thanks to these four key lessons we've learned over the years.

Give each other space to grow

We married when we were still growing and changing rapidly, which could have spelled disaster for our marriage.

But it taught us very early on that we need to allow one another space to change and grow as individuals. Our dreams and goals have shifted over the years, and that's OK, because we know that long-term relationships require flexibility.

Develop good communication skills

Neither of us grew up in households that prioritized healthy, open communication. So we had to learn how to articulate and problem-solve together.

We often listen to podcasts on relationships or read books that help us become better at communicating. We acknowledge when we get it wrong and always commit to learning how to communicate more successfully.

Don't let gender roles get in the way

Neither of us questioned gender roles when we got married, but once we had kids those cultural norms became a big issue in our marriage. We had to unlearn our ingrained assumptions about who does what and negotiate a more equitable partnership.

Creating an equal marriage has allowed my husband to feel more involved and present in our shared life and has given me the space and time to expand my career. Life is more enjoyable when you truly treat each other as equals.

Be nice, seriously

I truly think the backbone of our relationship is that we have always committed to being kind to each other.

We don't raise our voices. We don't name-call in hurtful ways. We generally steer clear of sarcasm, and we definitely apologize when we accidentally hurt each other's feelings.

That doesn't mean that we're always on the same page or that we never fight — it simply means we prioritize being kind over "winning" an argument.