Hidden Jealousy....?

In July, I was friends w/benefits/FwB (except with a few conditions) with this one guy, and we were close friends. Sometimes, either of us would think into consideration of dating each other, but we both kept our thoughts to ourselves and didn’t want to ruin of what we had so far. We remained close, until around November, we both seemed to kinda fall for each other slightly. Even though it was No-Nut November, we both still wanted to do things to each other, but at the same time, we expressed our feelings to each other and reciprocated. We never came out as a true couple, but we both ended up taking each other’s virginities and had sex for the first time regardless of our conditions. One day, we both decided to remain as FwB, but it seemed that afterwards, I didn’t want that. I actually wanted to stay warm with him and be with him. Recently, he started talking to this one girl (who’s also my friend) and they barely knew each other and just fell for each other in less than a week. I know that I lied about being “cool” remaining as FwB, but no matter what, I can’t help but to contain my emotions and it just upsets me whenever I see him with another girl. I feel like I got dumped, but I never dated him. I just can’t help but feel slightly terrible about lying about how I felt, or feeling jealousy as I don’t usually do.