Ok so my dad has had mental health problams for as long as I can remember, but in the last year its gotton worse somehow!? he won't even let me in his house (I live with my mum)or give me a cuddle the only time he's in a good mood is if he's had something to drink... but even then he's moody and annoying- although I would love to just spend 5 minutes with him he makes it seem like he hates me.
I miss my old dad so much and I feel so depressed my mum doesn't understand.Can I in someway help him or just make him realise what he's missing?

Mental illness if a sad thing that unfortunately affects everyone around the inflicted.

I wish there was some magic button I could push that would cure his illness and have him welcome you with open arms, but I'm afraid a button doesn't exist.

Just remember that his behavior is not your fault.

You need a father's love and he can't give it. You are fortunate to have one parent's love; many don't have any. Maybe you are old enough now to see if you can be HIS parent for a while.
Sometime when he will let you in and isn't drinking, take his hand and ask him what he was like when he was little, what his mother and father were like back then, what he missed or loved about them and about growing up. Gently let him talk. If he won't, don't push it. You tried. It's not your fault. Concentrate on what you do have.

Will, it's really a normal situation you have here cause I had the same problem but you know what I did? I stayed with my mom for a while without mentioning dad. After one month he started to call my mom about me and how he'd missed me and how much he want me to be there with him. So all what you have to do is stay away from your dad for 1 month or 2 weeks if you want then am sure he'll realize that he'd missed you and that he wants you back again. Do it you've got nothing to lose :)

I wish it was that simple:( , I tried to see my dad but as I said he wouldn't even let me in his house:(

When one has a mental illness unless it gets dangerous where he is committed for help, there is little family can do.
One can hope in years to come he will find help for it

How long ago was the divorce?

I think it is a safe thing to assume, that he does love you. The problem is, he does not show it, and even though he knows a simple hug would go a long way, he pushes you away.

Why likely has to do with shutting everybody out- he does not wish to change. It is easier to not deal with the emotions and needs of others, because he has been unable to deal with his own emotional needs, except, only through a bottle.

It is much simpler that way. No expectations.

For him to let you in, would mean he is opening himself up. You would become aware of how he is thinking, behaving, and living. All that he keeps now, to himself, would suddenly become larger than life, because one thing would naturally lead to another.

For example, if you were to go over and cook dinner for him, he may feel that the dinner conversation that would follow would naturally be centered around things he does not wish to disclose, share, or deal with. At the moment, dinner for one out of the microwave, seems a better alternative than meaningful conversation that does not break that comfortable place where he resides- alone.

Try to think of his rejection of you, not fueled by hate, but rather by, him not being willing to allow anybody in, because it would mean changes. He is simply not willing to change.

His mental health issues I can't address, because I don't know if that is just an observation on your part, or if he has at some point been assessed professionally to determine what mental health issue(s) he has. If he has been diagnosed with a mental health problem, and he is on medication, it doesn't sound like he's been attending counselling, or follow-up visits. Otherwise he wouldn't be adding alcohol to the mix to elevate his mood.

All you can do in my opinion, is keep in touch, even at arm's length, via email, and on his birthday etc. and he will know that when he can handle his own problems, only then can he make the decision to have a more substantial relationship with you- or anyone else.