Hi Angela
I disagree with earlier posts. I dont think he is necessarily looking to cheat, they may well be cries for help...in an inappropriate way admittedly.
Basically I think the core issue here is your b/f is desperately seeking attention from you - and I dont blame you or anything - but often when a couple have a young child in the first 12 months, the man can often feel left out. Many marriages split at this stage due to this issue, having a child can expose and widen cracks in relationships or conversely bring people together. Either way, a young child presents a huge demand on any relationship.
In other words, a young child changes the dynamic of a marriage so much. Clearly theres 3 of you now and the baby demands so much time from their mother - this can make the man feel isolated and some may start to look elsewhere for attention. Finding quality time together is so vital.
Now that isnt to say that he should be doing what he's doing re: internet, etc. But I think its a cry for help and a cry of frustration on his part - at least he isnt out there actually seeing someone, he's doing this stuff at a distance which makes me feel its a cry for attention.
Clearly, you will be both tired with the new baby, and Angela you have anxiety issues, so communication isnt going to be ideal anyway at this time. Nonetheless a frank discussion, either with or without a councellor, needs to be had about why he is behaving the way he is and what his (and your) needs are. Do you get quality time together as a couple very often?
I dont think this relationship is beyond repair, it can be fixed relatively easily if both sides needs/values are listened to and compromises made. Clearly some forgiveness will be needed around the issues you raised but this is by no means irrepairable as I think the root cause is him feeling his needs arent being met (from his perspective) due to the changed dynamics of your relationship with the new baby.
Hope this alternative perspective helps
King