Weird situation with ex and new love interest

Ive recently started speaking to my ex again and we’ve been meeting up and we’ve even stayed the night around each other’s houses. However, we haven’t officially said that we’re back together and he said he wants to take things slow.

While we weren’t speaking (1 year), I ended up speaking to other guys and i was speaking to one particular guy on and off. This particular guy would message me every now and again and I’d never really think too much into it until pretty recently when he sent me a message asking me out on a date. Im not sure whether to pursue things with him and completely stop things with my ex or whether I should just end things before they’ve begun with this new guy. I feel so guilty for even speaking to any other guy other than my ex right now but this new guy has things a lot of common with me in terms of interests whereas i know im completely comfortable around my ex.

Id appreciate any advice as ive spoken to friends but id like a unbiased opinion.