Is my girlfriend hiding something / cheating on me?

Anything is possible. Once lying and/or cheating enters a relationship, it's very difficult to ever fully trust that person again, even if you love them. She's so controlling and jealous of you, which is a sign that she, herself, is doing something and feels guilty about it...so projects it onto you. BE VERY CAREFUL! You don't want to commit to her until you know for sure the baby is yours. Otherwise, you will be raising another man's child for the rest of your life, and chances are good that your girlfriend will let this guy into the child's life IF he's the father. You have every reason to be suspicious. However, between her controlling nature and jealousy...and you checking her phone and being suspicious of her (tho justified), you and she are headed for a disastrous relationship. First, you need to make sure this baby is yours...then decide what you're going to do as far as your girlfriend. Don't set yourself up for pain and failure by committing to her just because of a baby...you can still legally be part of the baby's life without being her (girlfriend) puppet