3rd wheeling a friendship

In my college I was friends with this girl that I really liked and very good friends with this one guy that was awkward in talking to girls, as time goes on of spending time with them seperatly we start to develop deep bonds, however one day I was playing with my m8 and the girl I liked asked me to play, so I thought it was a good idea to let her play with us since that way my friend could practice not being nervous around them. As we start to spend full days on calls together we get closer all together, but I start to get jealous of their friendship because she started wanting to play with him more often. Some time past she is being very clingy with my m8 and since she is the girl I like I kind of get upset, and she just reassures me saying that she has no favorites, but even more time passes and she tells us that he was her favorite, and that made me feel like shit because it's not the first time that this has happened and second I was the one that started this friend group, and now they spend most time together and cuddling and every time I go near I feel like a third wheel. And this is making me really depressed because she ment the world to me and now she prefers another guy.