How to Bring the Excitement Back to a Relationship

We used to have so much fun together, never fight, perfect couple. We met and immediately clicked. Couldn't spend a moment apart. We did everything together. We were so happy. There was no tension. We showed each other off.

Now it's been 3 years and we have a baby. That spark is gone. We fight constantly. There have been multiple times he's fallen for other women and talked to them/sexted them. He's never had sex with someone else (not that that makes a difference to me. Emotional cheating feels worst).

We've always been best friends but I'm having trouble refreshing our relationship and forgiving him. Now there's so much strife.

I know it's completely normal for relationships to change over time and to lose that "honeymoon phase" but I'm willing to do anything to spark up that same passion, love, and fun we had when we first met.

What can I do? We have a great sex life so it's not that. How can I reignite that spark?