Do I have enough to assume he's smoking?

My boyfriend smoked for 11 years, he said he would quit because we have a baby on the way and it’s not healthy for us. He said he quit for 10 days and everything was good. We ended up getting in a fight about something which apparently ‘stressed’ him out so he gave in and had a smoke, at first he didn’t tell me, I had to confront him.

I think he’s smoking again but everytime I talk to him he claims that I don’t have enough proof for accuse him of doing so. Here’s why I think:

1. All of a sudden he’s taking walks every few hours that he never used to take, although he had a broken foot and the doctor said he needs to stay active. BUT - sometimes I go for walks with him and he still ends up going for one a little while after.

Tonight we went for a walk before bed because he said he was about to go for his ‘nightly walk’ so I said I would go with him to take my dog for some fresh air. We ended up staying up for a couple of hours and I said I was going to bed and he was like “if you wake up in a bit and I’m not here I’m just gone for a walk”… wtf, didn’t we go for his ‘nightly walk’ together?

2. All of a sudden hes chewing gum every time he comes in from his walks, he NEVER used to chew gum before.

3. If he’s not chewing gum when he gets back, he’s right upstairs brushing his teeth.

I mean, something must be up, right? He tries to make me look stupid and denies things until I prove myself. I don’t know how much longer I can deal with this, I hate feeling like someone who ‘loves me’ is doing something behind my back.