Thank you all for your comments. My minds whirling and I'm so tired of over thinking but I hope this post will be clear. If anything it will help me put things in perspective.
I spoke to DH. I came in from the garden and asked him to have a coffee with me before he went on his walk.
I'm afraid I chickened out on telling him I looked at his phone, I do feel ashamed about doing that.
I just told him I was worried about him as he appeared distant and not himself. I asked him if he needed to tell me/discuss anything with me. He didn't know what I was talking about, said nothing was wrong, he wasn't distant etc...
I said that I felt things had changed between us, he just said he loved me, nothing was wrong, he's just tired, busy, usual stuff, but nothing to worry about.
I suggested that maybe we should forget the garden, and his walk and go out for a family meal, have some time together which he agreed on. It was too late to get a babysitter but we all went and had a lovely time.
We have been together for twenty years, married 14 years. He is my best friend, I'm his. He has been so devoted to me over the years, overly generous and always there for me.
We have had our children in quick succession, so it has been very busy and tiring and I know our relationship has suffered. We have discussed about making more of an effort, going on dates, but probably don't do this enough. The reality is that it's expensive to get a babysitter, both of us tired in an evening and we usually end up getting a takeaway instead.
Since he has been acting 'distant', I have tried mentioning going out more, making more time for us but he doesn't appear that enthusiastic, just shrugs and says 'yeah, ok'.
About two years ago he took up running. He usually runs with a friend (male). They have done a couple of marathons. He tries to do this at least twice a week, during the day or evening, whenever he can.
I have really encouraged this as he has never really had any hobbies, and think he sees it as a release from children, chores etc.
There was some family upset a year ago, a family member aimed some anger at me, but DH completely stood by me and supported me at the time.
I may be going mad, or just paranoid but I think something isn't right.
I have been with this man for twenty years, and know that something has changed. I just hope it's not his feelings towards me.
I've decided to just keep watchful. I'm going to try and make more of an effort, and work on being a couple again.