Questioning my Relationship: Is My Boyfriend Cheating on Me?

I think my bf may be cheating on me he said he has to go to the office to do paperwork that his Sargent needs filed out b4 the morning... we went out tonight and had an amazing time till he said that .... I'm really questioning alot with our relationship right now we keep fighting alot and keep disagreeing alot on things that really matter my mental health has been taking its toll on both of us I was just recently in the psych hospital and in there they were telling me to share how I'm feeling and what I'm thinking and to not let ppl talk down to me or walk all over me anymore ... not that he does but there r times that he's made me feel like I'm not good enough and to fight for what I want cause my mental health needs it I just really need some help and guidance on this please any one with any words that may put my mind at ease