I have seen a solictor and he predicts settlement of between 50-60% to her including my pension.
If she's playing away, and this is what your solicitor said, you need to get a better solicitor! Do not ignore your happiness, unless you can look after yourself you will be useless at looking after anyone else!
I know of 2 or 3 men that have had similar situations, and though it was painful and quite costly (though not as costly as 50-60% of everything), they ended up keeping the family home and getting primary custody of the kids in each situation.
One useful trick in each case was that they managed to get the house seriously undervalued, meaning that buying her out of her half was cheaper than it should have been in each instance. Getting a house valued properly costs money, so if you can get it done independently but get them to really undervalue it, she's probably not going to want to fork out cash from her own pocket to go and get it valued again, when it may well only get valued at the same low value again. Sneaky trick but well worth it!
Another quick trick, change the locks on the house whilst she's out. Then remove her belongings. She left you, you're well within your rights to insist she leave really.
Regarding the kids, it ain't gonna be easy of course! The likelihood is that the 15 year old will understand though, the 12 year old will understand fairly quickly, and the 5 year old is too young for it to really have much affect on yet. Whatever you do you must explain to them that whilst their mother and father don't get on at all any more, you would not try to get in their way of having a relationship with their mother, and you must not try to influence the way they feel about her. They will most likely feel quite let down by her for playing away from you anyway!
Most men lose out in cases like these by not standing their ground. Women are much more prepared to fight in these situations usually than men are, hence they often win even if they've been the ones to play away. Stand your ground, let her know she's the one that's at fault, and obviously let the courts know too! Prove you're a decent father, capable of looking after your children on your own if needs be, and you should be ok.
Unless there's anything you're not telling us?