How to remain friends with your best friend when you have a crush on them?

Hi Guys, so I've been needing help with how to remain close to my long time best friend while they're also dating other people. For some background, we met in college and have been living together since. At first, I only liked them in a friendship way but over time I started to notice that I would feel jealous when people they were dating came over. I especially started to feel jealous when they got into a relationship with a person and they were really serious about this person. They have broken up since but now they are starting to go on dates again and getting to know people romantically again. It's been really hard to deal with since they are my absolute best friend and I spend almost all my free time with them. We are life partners and i don't want to lose them because of my insecurities or my feelings. At this point, I just want them to be happy and I want to be happy as well. I don't want to stop being friends with them or take a break from hanging out with them. I know that although today was fine, tomorrow could be terrible and I could be hurting. Any tips on how to remain by their side without feeling like I need to stop being their friend all together?