I've name changed for this.
Me and my boyfriend have a baby boy. When I was about 3 months pregnant I saw messages on his phone and I broke up with him straight away and he got with her. A few weeks before I gave birth he apologised and told me he shouldn't have cheated. When baby was born I let him see him and he asked if we could try again with our relationship, I said yes but I told him it'd be his last chance and so far our relationship has been good and he lets me go on his phone etc so I know I can trust him. Yesterday, she messaged me saying he was cheating on me and messaging her flirty things. I asked him if I could go on his phone (but I didn't tell him why I just said mine was charging). He let me and the only messages were that she asked him if he was bored of being a dad yet and he said no, she then told him that she missed him but he didn't reply to that.
He didn't tell me that she messaged him but would you find this suspicious or would you just assume she's trying to cause trouble and make us split up again?