Lying or telling the truth?

[nightowll]

Me and my ex have been speaking about getting back together, I’ve had my suspicions he is seeing someone, I mentioned this to him over text and all I got was “you don’t know what your on about” and that was it. I told him I didn’t want to speak to him again and felt like I didn’t know who he was anymore, he didn’t reply.

He’s picked dd up this morning and said nothing about the girl I mentioned, and has acted like everything is fine, I asked if he wanted to collect his last few bits or I’ll put them in the garage and he said no he’ll get them another time and not to be a dick!

The way he has acted does it seem like he most likely is seeing her?

He hasn't denied it though, has he?
He might be seeing someone in a casual way, he might be waiting to see if if you and he get back together, not wanting all his eggs in one basket.
What is he doing to make you think you might get back together?
If you split up because of his cheating, and he's still seeing the same person, that's different to him dating casually after you ended the relationship definitively.
Really, we'd need more background to be able to say anything useful to you.

We can’t possibly know if he’s seeing her, but it does sound like getting back together would be a bad idea.

His response in the text seems dismissive. His later actions suggest he has decided it's pointless to try to convince you he's not seeing her, because he thinks you don't trust him. Whether you have good reason not to trust him is anyone's guess.