A big factor, listening. I just listen to her when she talks. I can name every friend she's had, ex's (this one sucks, but I asked), her parents and family. I remember her b-day, debit card code, days big events occurred in her life.
Surprise random thoughtfulness!! Show up at her job with flowers, her fave drink, or snack. Random funny text to brighten up her day.
All kinds of stuff mate. In moderation of course. Do these everyday and it becomes stale and boring haha. Man love takes being creative. I hate it lol🙃.
For me it seems to help both ways to have sex often, cuddle a lot, talk intimately, build up trust in each other, look your best, stay in decent shape (energetic), keep a healthy dose of mutual independence but also balance it out with shared interests and mutual activities, and never fight -- always deescalate conflicts as soon as possible.
It helps to be there for each other when desired/needed and give each other some freedom and space when not. It's good to give each other a chance to miss each other.
And to me it helps if the two of you do things a lot like being affectionate towards each other only when you mean it, to not simply start saying and doing stuff to each other as a daily routine. That can make the act repetitive, losing it meaning/value and it's easy to start taking little hugs and kisses and words of affection for granted if you two just start doing it every day in a routine kind of way.
1. I keep expressing my love to her 2. Compliment her on things she does & the way she looks 3. Appreciate & acknowledge her gestures 4. Care & look out for her without making her feel suffocated or patronised Etc
By paying attention to their needs and desires and trying to anticipate what they might like. I'd also try to keep your relationship fresh via random acts of fun. But remember to always be yourself and not be obsequious- he or she is in a relationship with you for who you are, not for how good a servant you can be. And finally, make yourself happy- if he or she truly cares about you, they won't be happy if you aren't happy.
By being supportive of him and telling him every day that I love him and just being kind... I dunno, I think when you really do love someone all your little actions reflect that and they can sense it...
I am single, but if I had a boyfriend I would try to make him happy by listening to him when he wants to tell me about his day and the problems in his life. I would try to cheer him up when he is feeling blah and I would be affectionate with him.