advice SO cant stop lying!

My partner has an issue with lying and in my eyes cheating. I keep catching him out constantly on lies and doing dodgy stuff. our son is 14 months and in the last year I've caught several Snapchat accounts were he has messaging about 100 girls. caught him talking to one girl... nothing sexual just her telling him was good looking and to add her on Snapchat and then she asked did he have a GF and he didn't answer her back. in the last few weeks i caught him on POF and Tagged but I couldn't login to it fast enough to see what was on it... he lied and lied though his teeth for weeks on end and then finally comes up with excuse of tagged was download to check I wasn't cheating and he admitted he made a POf account but was just on it to try to delete it! anyways my point is he constantly lies about stuff like this and keeps making accounts. he reckons there's something wrong with him and he can't help it! he lies over stupid things too something as silly as me asking did he change the babies nappy.. he would say he did and I'd clearly see he didn't! it's got to the point where I'm drove insane and I just need him to realise what he's doing to me. he's only sorry when he's caught! I spoke to his family and they said he's always been the same and they don't know will he ever stop.. I just I'm at my whits end.. like he's making me aggressive and parranoid and I don't want to feel like this anymore especially not when we have our son witnessing it all!! I suppose I'm look for advice from anyone that's in this situation.. I love him so so much and I love being a family.. I'm thinking of looking for couple therapy. have anyone does this and has it helped? looking for advice please!