Help!

Hi ladies ive been with my boyfriend for 3 years on june we will be 4 years i live with him but like 2 months ago i caught him messaging a girl on fb and i got mad and when i confronted him about it all he told me was that "shes my childhood friend" i kinda had a feeling he was going to tell me some shit like that and ever since then ive been holding a grudge against him and our relationship hasn't been the same anymore sometimes i feel like I'm faking to be happy just so that i won't feel lonely.. im not sure if i love him anymore 😔 any advice would be really helpful!