OE is just a program to collect emails from any address, so don't understand what you mean by OE address unless you are meaning you have one account, in which case it won't be affected by making a new account for gmail.

In OE you have/make a separate account for each email address. example: If you have 3 email addresses you have 3 accounts in OE, the part after the @ is the name of the server where OE goes to collect that mail (note that it has nothing to do with who your ISP provider is)

I am with TalkTalk for ISP (I agree about losing internet connection regularly) also separately the TalkTalk email server is often out of action :(

I have 6 different email accounts in OE all are configured so that when I click on the Send/Receive button OE goes to each in turn and sends/collects emails. Or I can click on the dropdown arrow at side of Send/Receive button and do them individually. You prob won't have the dropdown button as you only have one account, it will appear when you make another account as will the choice of which email to use when you 'Create Mail' - dropdown at end of the From: on the email.

If you have a look in 'Tools' > 'Accounts', and highlight your email and then click on 'Properties' on the right > on the 'General' tab at the bottom there is a box to tick to 'include this account when receiving mail or synchronising'

Also I think in gmail webmail account (not in OE) you can configure it to collect your talktalk email which would then be collected by OE via gmail when you collected the gmail, but I have never used this as I figure if Talktalk email server is down gmail can't collect it either to send to me.