needsum advise

right well my ex left me for my best friend and they will b movin in together soon as she lives near me but my ex currently lives 55 miles away so he wants to b near his sons we have an 11 month old and im due to give birth in 4 days lol!!! he doesnt have our son over night at the min as i dnt trust him (but do have my reasons y) and in the past 4 weeks hes cum to see his son 4 3 n hlf hours n since we split has not provided at all for either of his sons.
hes said once he has moved he will help out more and b a proper dad to them which i really hope he does but i doubt it very much! but wat do i do wen he does move n wants to take them bk 2 his do i let him meet his gf bearin in mind they have only been tgeva 4 months and how do i knw they will be safe do i ask to see were hes livin b4 i let them go? i mean 1 good thing is at least i knw the girl hes with not that i particuly like her now but its better than him bein with some random person if u knw wat i mean? they wont be stayin over night until we have sorted something out about trusting again.
any advise would be great xxx