Greencar. Just something about mindfulness. I'm not a Buddhist but it's a practice I've been interested in for years. I read about it, have occasionally tried meditation, but find mindfulness more helpful.
I'm not sure I'd say you have to be relaxed to do it. It's more of a conscious decision and then a focus. For example, you've got to go shopping and all you can think of is the crap going through your head that he's been saying. You decide in that moment that he's not there, you don't need to "do" anything about the crap just now, just to focus on the present.
It feels very strange at first but you totally concentrate on what you're doing. In this case being very aware of your surroundings, what you're looking at, what you need. Every time you feel a thought crowding in you just kind of mentally flick it away. It takes quite a lot of practice, but the practice itself is useful.
It kind of changes your time frame as well. Sometimes you feel that he's occupying 100% of your life. But if you can break it down you realise it's a finite amount. I can see that what you're going through at the moment will literally, practically, occupy a large amount of your day. The trick (and I can't always do it) is to stop the mulling/thinking/going over part.
This is the bit that's there when you're trying to do all the other stuff in your life. Being mindful, for me, is remembering that there is a time and place to think/worry about this stuff. But for the here and now I'm with my dc, listening to music, walking, eating, whatever. It's not denial, or ignoring things, just letting them have their place.
I'm no expert by any means. This is just my personal experience. If you looked at someone playing the piano, it would be sad to think they weren't enjoying the experience because they were seething inside about some personal matter. It's about learning to enjoy what's really happening in "that" moment, the music, not the personal matter.
It sounds a bit weird but it's strangely calming. It makes you feel strong as well, like you have a bit of armour. It also makes you feel more in control.