I'm sorry to hear you're having such a tough time. It's probably not much consolation but my DD (also 25 weeks) has had a similar sleep/nap pattern for the past 10 weeks. Fortunately she doesn't need to be permanently latched on to stay asleep, but she does like me to be within touching distance at all times.
I posted here when I had reached the end of my tether and had some good advice and insight into our situation. My DD is basically caught in a vicious circle of horrific overtiredness. It prevents her napping properly and makes bedtime a real battle. She's unable to get to sleep or stay asleep except with constant help from me.
In the past fortnight her sleep has slowly started to improve. Last night she woke every 90 minutes instead of every 45, which makes a huge difference when you're on your knees with exhaustion. Here's what I've been trying:
-prioritising breaking the cycle of overtiredness above all else. I let her play for an hour and then feed her and put her in a sling until she naps. Sometimes she takes an hour or more to go off, and it's hard having a baby permanently attached, but it definitely helps. She's now taking 4 half hour naps a day. I am certain this is really helping her sleep better at night.
-introducing one small meal a day. My DD has reflux and I took medical advice before doing this. I'm not sure if it has really helped her sleep-wise but she absolutely loves food and it hasn't made things worse.
-accepting co-sleeping is the only way to stay sane. I now share a double bed with DD and DP sleeps in another room. She still wakes a lot but I can't even remember every wake up come the morning.
-taking better care of myself. I was starting to feel horrifically depressed about our situation. I tried to put on a brave face, kept getting up and heading out to baby groups, staying up to do the housework etc. I was so exhausted I started having hallucinations. I have temporarily given up all unnecessary activities to save my energy for looking after DD through the night. I try to eat fresh and healthy food, admit I need help and accept this is a phase that will pass.
The No Cry Sleep Solution is a good read if you would like to stop feeding to sleep and gently help your baby to self settle. Once my DD is a little less sleep-deprived I plan to try some of the techniques myself.
and
for you until things get better